<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        a
        {
            /* 鼠标经过时，文字颜色变成黑色 */
            color: black;
        }
        a:hover
        {
            /* 鼠标悬停时，文字颜色变成红色 */
            color: red;
        }
        a:active
        {
            /* 鼠标按下时，文字颜色变成绿色 */
            color: green;
        }
        body
        {
            font-family: "microsoft yahei";
            background-image: url(118291522_p0_master1200.jpg);
            background-repeat: repeat-x;
            background-size: cover;
            background-position: center;
            background-attachment: fixed;
            div 
            {
                width: 200px;
                height: 200px;
                border: 2px solid green;
                border-radius: 100px;
                /* 或者用 50% 表示宽度的一半 */
                border-radius: 50%;
            }
            
        }
    </style>
</head>
<body>
    <a href="#">百度</a>
    <!--  -->
</body>
</html>